The present invention relates to a series of improvements introduced in airvessels used in molding expansive waves, which molding system is specifically used to conform sand molds used in casting.
This system essentially comprises introducing the sand, which falls from a chute due to the effect of gravity, into a mold box where it will be compressed due to the effect of air under pressure supplied thereto from a vessel, specifically from the vessel on which the invention is focussed.
The mold box of the molding system cited in the previous paragraph is fitted with a framework and is assembled on a table which may be displaced vertically, so that when the table is raised the mold box couples hermetically against a diffuser positioned under the vessel.
When the valve connecting the vessel and the diffuser is opened, air from the vessel enters the latter abruptly and acts on the sand which constitutes the mold, compressing same.
One of the solutions for the practical embodiment of this molding system consists in the valve located between the vessel and the diffuser, i.e., the release valve, comprising a stiff plate or disc which remains closed due to excess pressure inside a chamber where said plate plays, so that when the excess pressure disappears from said chamber, the air under pressure accumulated in the vessel can displace said closure plate towards an open position and enter abruptly into the diffuser, falling upon the sand and causing it to be compressed. When air under pressure is once again introduced into the said chamber where the plate constituting the plug or valve element plays, such plate again moves towards a closed position.
When the valve is closed, residual air under pressure, which must be eliminated, remains in the diffuser, thereby causing one of the major problems of this system. More specifically, the residual air may not be eliminated through the centre of the valve towards the vessel and from the latter to the exterior, and it must therefore be released through some side conduit provided in the framework or near the mouth of the diffuser, i.e., at all times through a conduit located near the sand mold. This causes extremely abrasive sand particles to be dragged by the residual air when it is released, and such sand particles will damage everything they find on their way.
Another disadvantage of this system lies in the fact that, bearing in mind the nature and operation of the valve, the disc causes brusque collisions and therefore noise, when changing from a closed to an open position.
Another known solution consists in using a butterfly type valve, i.e., a mechanical valve which is consequently slower when reacting than the previous valve, or at any rate reacts accordingly to what it is.
This solution, like the previous one, has the disadvantage that the residual air present in the diffuser cannot be extracted through the centre of the valve towards the vessel, and must be released through side conduits located in the framework.
Another known solution consists in the release valve comprising two superposed discs provided with openings which will allow or prevent passage of air under pressure to the diffuser, depending on whether or not the openings of one disc face the openings of the other disc. The main disadvantage of this solution is that the valve is evidently mechanical and reacts as such.